1. Field of the Invention
The present invention relates to a vehicular air conditioner for controlling a cooling means and a heating means to adjust the temperature and humidity in a passenger compartment without fogging the window glass.
2. Description of the Related Art
Vehicular air conditioners have in combination an evaporator for cooling and dehumidifying air by utilizing the heat of vaporization of a refrigerant and a heater for heating air with the heat of an engine coolant to adjust the temperature and humidity in the passenger compartment of a vehicle.
If the vehicular air conditioner is controlled to lower the cooling ability of the evaporator at a low atmospheric temperature, then since the dehumidifying ability of the evaporator is also lowered, the water vapor in the passenger compartment is possibly condensed on the window glass, etc. when the atmospheric temperature is low and the atmospheric humidity is high.
To eliminate the above drawback, a conventional vehicular air conditioner for keeping a sufficient dehumidifying capability to prevent the window glass from fogging due to condensation, and also for preventing unnecessary cooling thereby to save energy has been developed (see, for example, Japanese Patent No. 3298151 for details).
The conventional vehicular air conditioner estimates the temperature of the surface of a window glass and calculates a necessary humidity of ejected air which represents the humidity in the passenger compartment that will not cause window condensation at the estimated temperature. Further, the conventional vehicular air conditioner determines a dew point of air which represents the calculated necessary humidity of ejected air, and sets a lower temperature of a necessary temperature of ejected air and the dew point as a control temperature of the evaporator for controlling the temperature in the passenger compartment at a preset temperature. The conventional vehicular air conditioner uses a preset humidity in the passenger compartment and humidity in the passenger compartment which is detected by a humidity sensor installed in the passenger compartment for the calculation of the necessary humidity of ejected air.
If the temperature of ejected air that is necessary for controlling the temperature in the passenger compartment at the preset temperature is lower than the temperature of ejected air that produces the humidity in the passenger compartment that will not cause window condensation, then since the humidity in the passenger compartment is high even if the temperature in the passenger compartment is close to the preset temperature, the passengers in the passenger compartment may feel uncomfortable.
If the humidity in the passenger compartment is lower than the humidity which causes window condensation, and the temperature is lower than the present temperature entered by the passengers, and the humidity is lower than the humidity which makes the passengers feel uncomfortable, then since the passenger compartment does not need to be further cooled or dehumidified, there the cooling ability of the evaporator may further be controlled in order to save energy.
If the humidity of exterior air that enters the passenger compartment is not taken into account in the process of determining the temperature of ejected air that produces the humidity in the passenger compartment that will not cause window condensation, because the necessary humidity of ejected air cannot be calculated highly accurately on account of a humidity change caused by the humidity of introduced exterior air, the cooling ability of the evaporator may possibly be excessively controlled or the necessary amount of dehumidification cannot be obtained.